1. Field of the Invention
This invention directs itself to a method for laser engraving of photopolymer printing plates. In particular, this invention directs itself to a method for laser engraving photopolymers normally utilized in a chemical etch process, which are then prepared by the inventive method for laser ablation. Further, this invention directs itself to a method for laser engraving which includes steps for removing polymer particulates, previously molten by the base ablation and which have become attached to the upper surface of the engraved photopolymer printing plate, prior to the final finishing thereof.
2. Prior Art
Methods of laser engraving are well known in the art. The best prior art known to the Applicant include U.S. Pat. Nos. 5,075,365; 3,549,7913; 4,898,752; 4,877,481; 4,909,895; 5,011,567; 4,323,928; 4,934,267; 4,894,115; 4,897,153; 4,925,523; 3,755,646; 4,379,022; 4,661,201; and, 3,742,853.
In some prior art systems, such as that disclosed by U.S. Pat. Nos. 3,549,733 and 4,898,752 there is disclosed methods for laser engraving printing plates and the problems associated therewith. These disclosures note the problems associated with laser engraving flexographic type plates, that is the production of residue or a ridge surrounding the depressed areas when soft polymer materials are utilized. In particular, it is noted in U.S. Pat. No. 4,898,752 that laser engraving of photopolymer plates result in mottled printed surfaces, and therefore the disclosed method utilizes a rubber material having a Shore A hardness of 55 or less. U.S. Pat. No. 3,549,733 suggests two possible solutions to the problem, the least practical being the use of a laser beam of sufficient intensity so as to vaporize the material without producing any melting, but then goes on to say that this method would be virtually impossible. The preferred solution, suggested by this reference is the use of a particular material, an acetal resin such as DELRIN which could be engraved without forming any ridge around the depressed areas. However, neither of these disclosures suggest methods by which the photopolymer material, widely used to produce flexographic printing plates, and the associated photopolymer processing equipment, could be utilized in a laser engraving process. Flexographic printing plate manufacturers have a large investment in materials and equipment for chemical etch processing of photopolymer plates, which can be utilized to produce laser engraved flexographic printing plates by the method of the instant invention.
In other systems, such as that disclosed by U.S. Pat. Nos. 4,877,481 and 4,909,895 there is disclosed methods for removing residue or ridges adjacent laser engraved surfaces. Although these disclosures are not directed to laser engraving of flexographic printing plates, they note the formation of a residue resulting from laser ablation. The disclosed processes solve the problem by adding a coating layer to the surface of the material to be laser engraved, and then remove the coating layer subsequent to laser engraving, to thereby remove the residue therewith. Whereas in the method of the instant invention a process for removing the residue without the addition of additional coatings is provided, thereby providing a more efficient process. The novel method of the instant invention providing an economical method for providing high quality laser engraved photopolymer printing plates.